Purifying gases



Feb. 5,

` E. PlRoN PURIFYING GASES Filed Jan. 7. 1925 :NVE/WOR.

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UNITED STATES PATENT OFFICE.

Emir. Pinon, or YORK, N. Y., Assrenoa 'ro Pinon COAL DisrILLArIoNSYSTEMS, INC., or NEW Yoan, N. Y., A CORPORATION or DELAWARE.

PUBIFYING GASES.

Application illed January 7, 1925. Serial No. 957..

In wood distillation the condensable prod` ucts from the wood retortsare roughly classified into two products, viz, the nonaquerous,including the various light oils and tar collectively termed tar, and anaqueous portion containing acetic acid, met-hyl alcohol, acetone andother substances including water itself, known as pyroligneous acid orgreen liquor. Heretofore it l0 has b een customary practice to condenseboth pyroligneous acid and tar (including the light oils) together,allowing the aqueous and non-aqueous portion to separate and then todecant one layer from the other. It

is not practicable, however, to fractionate the separated pyroligneousliquor directly, due to the fact that the separation of the tar is nevercomplete and the tar present, clogs the condensing and fractionatingapparatus. It is therefore necessary irst to subject the entirepyroligneousacid to a preliminary distillation in order to eliminate taras much as possible.

Due to the` expense involved in this preliminary distillation step,numerous methods have been roposed oreliminating the tar from thedistillation gases prior to the condensation of the pyroligneous acid.In all of these methods, some tar scrubbing medium is used, but so faras I am aware, none of these methods has been entirely successfuldueftothe fact' that a slight amount of tar or tar-forming material is left inthe pyroligneous acid vapors which, however small, will gradually plugup the plates of the distilling columns and render cleaning necessary atfrequent intervals. It is my belief that the presence of tar in the acidproduct is due to the presence of tar-form- 40 ing substances whichelude condensation or absorption by the scrubbing medium and thattherefore, itis not practicable to remove all the tar by purely physicalmeans alone. v

In accordance with my present invention,.

I preferably subject the distillation gases (by which term it is, ofcourse, meant to include what, strictly speaking, are vapors) toapreliminary washing operation, using a known scrubblng medium, wherebythe major portion of the tar is removed from the gases, or, if my theoryis correct, perhaps all of the tar then present in the gases as such. Ithen subject the gases, while maintaining them at a suitabletemperature,

@5 to vthe actlon of one for r`more substances which I have found will4eiectively remove all the remaining tar and tar-forming elements,whereby the pyroligneous liquor obtained will be substantially entirelyfree of tar. The substanceslwhich I have found to possess thistar-removing property are, first, those which exert a moderately strongoxidizing action under the conditions present (it should be kept in mindthat the retort vapors are strongly acid), and, second, acids which arenot volatile under the pressure and at the temperature prevailing in thescrubber. Among the first class yof substances I may mention chlorine,potassium permanganate, potassium dichromate and hydrogen peroxyde,while in the second class, sulphuric, `phosphoric and oxalic acids havebeen found effective. I greatly prefer, however, sulphuric acid ofsuitable concentration as the sole scrubbin 'medium, since it is notonly an acid which meets the abovenamed requirements as an acid, but itis l also an oxidizing agent aswell, soy that b using sulphuric acidalone I obtain as goo if not better, results as those had by using aseparate oxidizing agent and a separate acid. It will be'understood thatthe tar may be removed by the oxidizing agent alone, but I have foundthat the action` of such agent is not `only facilitated by the presenceof the acid, but the character of the tar separated renders it moreeasily removed from the scrubber. It now seems that the action of thetwo classes of substances is that the oxidizing agent initiates theconversion lof the tar-forming substances into tar while the acid actsas a catalyzer in such reaction.

As above stated, I preferably remove the greater part of the tar by apreliminary washing or scrubbing with a medium having no appreciablechemical effect upon the tar itself; however, if desired, all of the tarmay be removed in one scrubbing step, as by scrubbing with sulphuricacid of the properconcentration alone or by scrubbing with other mediain the presence of sulphuric acid or the other substances I havementioned. In this case, however, the tar obtained will be contaminatedwith the special scrubbing material used and in general must be searated from it, as by neutralization,

etc. or this reason, I prefer to remove the tar in two or more steps, asstated.

The accompanying drawing illustrates diagrammatically one arrangement ofapparatus suitable for carrying out my improved method. In thisarrangement the distillation gases from the retort are first passedthrough what I have denominated a green liquor scrubber, in which thegases are scrubbed and deprived of a large proportion of their tar usingordinary green liquor or crude pyroligneous acid as the scrubbingmedium. This liquor is recirculated through the scrubber which ismaintained at a temperature above the boiling point of the pyroligneousacid. Of course, some of the green liquor is evaporated, but enough isused so as to accomplish a thorough scrubbing.

From the green liquor scrubber the gases pass to what I have designatedthe sulphuric acid scrubber. Prior to their introduction to thisscrubber, I generally iind it necessary to raise the temperature of thegases and do so preferably by mixing therewith a sufiicient quantity otheated uncondensable gases from the condenser and thereby prevent thetemperature of the gases being lowered to a point below the condensationof the pyroligneous liquor constituents. In practice, I have found itsatisfactory to maintain the temperature within the sulphuric acidscrubber slightly above 100 C.. so that the concentration of thesulphuric acid solution remain at about 30 Be. It will be noted that thetemperature of the scrubber determines the strength of the acid, since,if a strength of acid is used which has a higher Aboiling point than thescrubber temperature, water will be absorbed from the vapors until anacid of this boiling point is reached, whereas if the acid has a boilingpoint lower than the scrubber temperature, water will evaporate untilthe boiling point of the acid mixture corresponds to that of thescrubber temperature.

After the acid has recirculated sutliciently, it is drawn o" andseparated from the tar by decantation, whereupon the acid may be usedover again. If desired, this separation step may, of course, be madecontinuous. Some of the acid combines with impurities of a basic nature,but the amount ot' such impurities is relatively small.

From the sulphuric acid scrubber, the gases -pass to a condenser wherethe pyroligneous acid is condensed. As shown, the residual gases areconducted from the condenser by means of a suitable exhauster and areled back to be burned beneath the retorts or for other disposition. Aportion ofthem is passed through a reheater and then introrenderingprohibitive the cost of a prelimi-- nary distillation thereof for-thepurpose of removingthe tar. In my method, however, this step isobviated. A further advantage of the improved method is that it permitsthe direct fractionation of the pyroligneous acid into acetic acid andmethyl alcohol without previously neutralizing the acetic acid. Moreoverit gives a liquor from which Yan acetate of lime of higher concentrationcan be obtained.

I claim: Y

l. In' the art of wood distillation, the method of removing tar andtar-forming elements from distillation gases which consists in washingsaid gases with a solution of sulphuric acid while maintaining thetemperature of the gases above the condensing point of the nontarvapors.

2.' In the art of. wood distillation, the method of removing tar andtar-forming elements from distillation gases which consists 1n washingsaid gases with a scrubbing medium having substantially no chemicalaction upon the tar constituents to remove the greater portion thereof,then scrubbing said gases with a sulphuric acid solution whilemaintaining the temperature ot' the gases during said scrubbing stepsabove the condensing point of the nontar vapors.-

3. In the art of wood distillation, the method of removing tar andtar-forming elements from distillation gases which con.- sists inwashing said gases with a scrubbing medium having substantially nochemical action upon they tar constituents to remove the greater portionthereof, heating said gases then scrubbing said gases with a sulphuricacid solution while maintaining the temperature of the gases during saidscrubbing steps above the condensing point of the nontar vapors.

EMIL PIRON.

